Contact quality assessment by dielectric property analysis

ABSTRACT

Devices and methods for assessing tissue contact based on dielectric properties and/or impedance sensing are disclosed. In some embodiments, one or more probing frequencies are delivered via electrodes including an electrode in proximity to a tissue (for example, myocardial tissue). In some embodiments, dielectric parameter values, optionally together with other known and/or estimated tissue characteristics, are measured to determine a contact quality with the tissue. In some embodiments, dielectric contact quality is used, for example, in guiding the formation of a lesion (for example, RF ablation of heart tissue to alter electrical transmission characteristics).

RELATED APPLICATIONS

This application claims the benefit of priority under 35 USC §119(e) ofU.S. Provisional Patent Application No. 62/160,080 filed May 12, 2015;U.S. Provisional Patent Application No. 62/291,065 filed Feb. 4, 2016;and U.S. Provisional Patent Application No. 62/304,455 filed Mar. 7,2016; the contents of which are incorporated herein by reference intheir entirety.

This application is co-filed with International Patent Applicationshaving Attorney Docket Nos.: 66011 SYSTEMS AND METHODS FOR TRACKING ANINTRABODY CATHETER, 66142 CALCULATION OF AN ABLATION PLAN, 64488FIDUCIAL MARKING FOR IMAGE-ELECTROMAGNETIC FIELD REGISTRATION, and 66012LESION ASSESSMENT BY DIELECTRIC PROPERTY ANALYSIS, the contents of whichare incorporated herein by reference in their entirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to systemsand methods for probe positioning within a body cavity, and moreparticularly, but not exclusively, assessment of contact between anintra-body electrode and a body cavity surface.

RF ablation probes are in use for minimally invasive ablationprocedures, for example, in the treatment of cardiac arrhythmia. A highfrequency alternating current (e.g., 350-500 kHz) is introduced to atreatment region through the probe, creating an electrical circuitinvolving tissue, which heats up as it absorbs energy of the appliedelectrical field. The heating results in effects such as tissueablation. In the control of cardiac arrhythmia, a goal of ablation is tocreate lesions in a pattern which will break pathways of abnormalelectrophysiological conduction which contribute to heart dysfunction(such as atrial fibrillation).

One variable affecting the heating is the frequency-dependent relativepermittivity K of the tissue being treated. The (unitless) relativepermittivity of a material (herein, K or dielectric constant) is ameasure of how the material acts to reduce an electrical field imposedacross it (storing and/or dissipating its energy). Relative permittivityis commonly expressed as

${\kappa = {{ɛ_{r}(\omega)} = \frac{ɛ(\omega)}{ɛ_{0}}}},$

where ω=2πf, and f is the frequency (of an imposed voltage or signal).In general, ϵ_(r)(ω) is complex valued; that is:ϵ_(r)(ω)=ϵ′_(r)(ω)+iϵ″_(r)(ω).

The real part ϵ′_(r)(ω) is a measure of energy stored in the material(at a given electrical field frequency and voltage), while the imaginarypart ϵ″_(r)(ω) is a measure of energy dissipated. It is this dissipatedenergy that is converted, for example, into heat for ablation. Loss inturn is optionally expressed as a sum of dielectric loss ϵ″_(rd), andconductivity σ as

${ɛ_{r}^{''}(\omega)} = {ɛ_{r\; d}^{''} + {\frac{\sigma}{\omega \cdot ɛ_{0}}.}}$

Any one of the above parameters: namely κ, ϵ, ϵ′_(r), ϵ″_(r), σ, and/orϵ″_(rd) , may be referred to herein as a dielectric parameter. The termdielectric parameter encompasses also parameters that are directlyderivable from the above-mentioned parameters, for example, losstangent, expressed as tan

${\sigma = \frac{ɛ_{r}^{''}}{ɛ_{r}^{\prime}}},$

complex refractive index, expressed as n=√{square root over (ϵ_(r))},and impedance, expressed as

${Z(\omega)} = \sqrt{\frac{i\; \omega}{\sigma + {i\; \omega \; ɛ_{r}}}}$

(with i=√{square root over (−1)}).

Herein, a value of a dielectric parameter of a material may be referredto as a dielectric property of the material. For example, having arelative permittivity of about 100000 is a dielectric property of a0.01M KCl solution in water at a frequency of 1 kHz, at about roomtemperature (20°, for example). Optionally, a dielectric property morespecifically comprises a measured value of a dielectric parameter.Measured values of dielectric parameters are optionally providedrelative to the characteristics (bias and/or jitter, for example) of aparticular measurement circuit or system. Values provided bymeasurements should be understood to comprise dielectric properties,even if influenced by one or more sources of experimental error. Theformulation “value of a dielectric parameter” is optionally used, forexample, when a dielectric parameter is not necessarily associated witha definite material (e.g., it is a parameter that takes on a valuewithin a data structure).

Dielectric properties as a function of frequency have been compiled formany tissues, for example, C. Gabriel and S. Gabriel: Compilation of theDielectric Properties of Body Tissues at RF and Microwave Frequencies(web pages presently maintained atwww://niremf(dot)ifac(dot)cnr(dot)it/docs/DIELECTRIC/home(dot)html).

Dielectric properties comprise certain measured and/or inferredelectrical properties of a material relating to the material'sdielectric permittivity. Such electrical properties optionally include,for example, conductivity, impedance, resistivity, capacitance,inductance, and/or relative permittivity. Optionally, dielectricproperties of a material are measured and/or inferred relative to theinfluence of the material on signals measured from electrical circuits.Optionally, dielectric properties of a material are measured and/orinferred relative to the influence of the material on an appliedelectric field. Measurements are optionally relative to one or moreparticular circuits, circuit components, frequencies and/or currents.

Microscopically, several mechanisms potentially contribute toelectrically measured dielectric properties. For example, in the kHz-MHzrange, movement of ionic charge carriers generally dominates. In manytissues, cellular membranes play a significant role in thecompartmentalization of ionic charges. Conductance pathways are alsopotentially influenced by the cellular structure of a tissue. Dielectricproperties optionally are influenced by and/or take into accountnon-dielectric properties such as temperature.

SUMMARY OF THE INVENTION

There is provided, in accordance with some exemplary embodiments, amethod of characterizing contact quality of an intra-body probe with atarget tissue, comprising:

measuring dielectric properties of the environment of an electrode of anintra-body type electrode using an electrical circuit, the electricalcircuit being defined by the electrode placed intra-bodily so that thetarget tissue is included in the electrical circuit; and characterizingcontact between the probe and the target tissue, wherein thecharacterization of the contact comprises mapping of the measureddielectric properties to a mapped value within a range of valuescharacterizing the contact quality.

According to some embodiments, the mapped value comprises an indexcharacterizing contact quality.

According to some embodiments, the mapped value represents a contactforce equivalent, such that a force of contact of the intra-body probewith the target tissue is represented by the mapped value.

According to some embodiments, the range of values characterizing thecontact quality comprises at least four possible values.

According to some embodiments, the intra-body probe comprises anablation electrode configured for ablation of the target tissue.

According to some embodiments, the ablation electrode comprises theelectrode defining the electrical circuit.

According to some embodiments, the characterizing comprises evaluatingsufficiency of the contact for effective lesioning by the ablationelectrode.

According to some embodiments, the method comprises providing a userfeedback indicating the sufficiency of contact for effective lesioning.

According to some embodiments, the ablation electrode is configured forthe formation of a lesion in the target tissue by at least one of thegroup consisting of: thermal ablation, cryoablation, RF ablation,electroporating ablation, and/or ultrasound ablation.

According to some embodiments, the method comprises operating anablation electrode based on the characterization of the contact.

According to some embodiments, the operating of the ablation electrodeis gated to occur only when the characterized contact is within apredetermined range.

According to some embodiments, the characterizing contact is performediteratively during operating of the ablation electrode.

According to some embodiments, the operating of the ablation electrodeis based on an estimated contact force of the characterized contact,such that at least one of an ablation power, a duration of ablation, aselection of an electrode, and a frequency of ablation energy, isselected based on the estimated contact force.

According to some embodiments, the characterizing comprises estimationof an equivalent force of contact of the probe with a surface of thetarget tissue.

According to some embodiments, the estimation of an equivalent force ofcontact is substantially independent of an angle of contact between theprobe and the surface of the target tissue.

According to some embodiments, the characterizing comprises evaluating arisk of perforation of the target tissue by the probe.

According to some embodiments, the method comprises providing a userfeedback indicating the risk of perforation.

According to some embodiments, the method comprises moving the probeunder automated control based on the characterization of the contact.

According to some embodiments, the target tissue comprises cardiactissue.

According to some embodiments, the target tissue comprises cardiactissue of the right atrium.

According to some embodiments, the intra-body probe makes a plurality ofsimultaneous contacts with the target tissue, and the characterizingcomprises separately characterizing each of the plurality ofsimultaneous contacts.

According to some embodiments, the intra-body probe comprises anablation electrode, and wherein the method comprises operating theablation electrode to ablate at each of the plurality of simultaneouscontacts under separate control, based on the correspondingcharacterizing of contact.

According to some embodiments, the separate control comprises deliveryof a separately selected at least one of a frequency, phase, or level ofablation power to each of the plurality of simultaneous contacts.

According to some embodiments, the separate control comprises separatelyselected timing of delivery of ablation power to each of the pluralityof simultaneous contacts.

According to some embodiments, the characterizing of contact is based ona data structure mapping measured dielectric properties to acharacterization of contact with the target tissue.

According to some embodiments, the character of contact comprises atleast one from among the group consisting of: a risk of perforating thetissue with the intra-body probe, an estimate of contact force appliedto the tissue by the intra-body probe, and/or an assessment of adequatecontact for reliable ablation using the intra-body probe.

According to some embodiments, the data structure comprisesmachine-learned associations applicable to the measured dielectricproperties to convert them to the characterization of contact with thetarget tissue.

According to some embodiments, the dielectric properties comprisedielectric properties measured for a plurality of electrical fieldfrequencies.

According to some embodiments, the electrical field frequencies are in arange between about 5 kHz and about 20 kHz.

There is provided, in accordance with some exemplary embodiments, adevice for ablation of a target tissue based on dielectric contactquality of an intra-body ablation probe with the target tissue,comprising: the intra-body ablation probe, including at least oneelectrode; an electrical field measurement device, configured to measuredielectric properties in the environment of the at least one electrodebased on signals sensed by the at least one electrode; and a contactcharacterization module, configured to characterize contact between theintra-body ablation probe and the target tissue, based on the dielectricproperties measured by the electrical field measurement device.

According to some embodiments, the contact characterization modulecomprises a data structure mapping the dielectric properties tocharacterization of contact.

According to some embodiments, the device comprises a display configuredto display the characterized contact as an estimate of contact force.

There is provided, in accordance with some exemplary embodiments, amethod of indicating the orientation of a displayed view of ananatomical structure, comprising: displaying on a display an anatomicalview of the anatomical structure in a user-adjustable orientation; andcoordinating an orientation of a displayed schematic representation of aportion of the anatomical structure to the user-adjustable orientationof the anatomical view, such that the schematic representation isdisplayed in the same orientation as the anatomical view of theanatomical structure; wherein the schematic representation comprises abody portion representing a first part of the anatomical structure, anda plurality of protruding portions representing protruding portions ofthe anatomical structure and protruding from the body portion, such thatthe orientation of the plurality of protruding portions is identifiablefrom any orientation of the displayed schematic representation.

According to some embodiments, the anatomical structure comprises anatrium of a heart.

According to some embodiments, the body portion of the schematicrepresentation comprises at least two sub-portions; each sub-portionbeing distinctively shaded, and corresponding to a predetermined portionof the anatomical structure.

According to some embodiments, the anatomical view of the anatomicalstructure includes a view of at least one obscuring anatomical portionpositioned to obscure the predetermined portions of the anatomicalstructure, and wherein the schematic representation omits to representthis obscuring anatomical portion, thereby preventing obscuring of theat least two portions of the schematic representation.

According to some embodiments, each of the at least two sub-portions ofthe schematic representation corresponds to an atrium of a heart, andthe plurality of protruding portions comprise a plurality of generallycylindrical protrusions corresponding to the number of veins feedinginto each atrium.

According to some embodiments, the plurality of protruding portionscomprise a protrusion indicating a position of a heart valve.

There is provided, in accordance with some exemplary embodiments, amethod of characterizing contact quality of an intra-body probe with atarget tissue, comprising: measuring dielectric properties of theenvironment of an electrode of an intra-body type electrode using anelectrical circuit, the electrical circuit being defined by theelectrode placed intra-bodily so that the target tissue is included inthe electrical circuit; and characterizing contact between the probe andthe target tissue, wherein the characterization of the contact comprisesconversion of the measured dielectric properties to an equivalentcontact force estimation, and wherein the estimation of an equivalentforce of contact is substantially independent to an angle of contactbetween the probe and the surface of the target tissue.

According to some embodiments, the substantial independence comprises achange of less than 10% through a range of angles of contact, and therange of angles of contact is within 45° of a central angle of contact.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit”, “module” or “system”.Furthermore, some embodiments of the present invention may take the formof a computer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.Implementation of the method and/or system of some embodiments of theinvention can involve performing and/or completing selected tasksmanually, automatically, or a combination thereof. Moreover, accordingto actual instrumentation and equipment of some embodiments of themethod and/or system of the invention, several selected tasks could beimplemented by hardware, by software or by firmware and/or by acombination thereof, e.g., using an operating system.

For example, hardware for performing selected tasks according to someembodiments of the invention could be implemented as a chip or acircuit. As software, selected tasks according to some embodiments ofthe invention could be implemented as a plurality of softwareinstructions being executed by a computer using any suitable operatingsystem. In an exemplary embodiment of the invention, one or more tasksaccording to some exemplary embodiments of method and/or system asdescribed herein are performed by a data processor, such as a computingplatform for executing a plurality of instructions. Optionally, the dataprocessor includes a volatile memory for storing instructions and/ordata and/or a non-volatile storage, for example, a magnetic hard-diskand/or removable media, for storing instructions and/or data.Optionally, a network connection is provided as well. A display and/or auser input device such as a keyboard or mouse are optionally provided aswell.

Any combination of one or more computer readable medium(s) may beutilized for some embodiments of the invention. The computer readablemedium may be a computer readable signal medium or a computer readablestorage medium. A computer readable storage medium may be, for example,but not limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. More specific examples (a non-exhaustivelist) of the computer readable storage medium would include thefollowing:

an electrical connection having one or more wires, a portable computerdiskette, a hard disk, a random access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (EPROM or Flashmemory), an optical fiber, a portable compact disc read-only memory(CD-ROM), an optical storage device, a magnetic storage device, or anysuitable combination of the foregoing. In the context of this document,a computer readable storage medium may be any tangible medium that cancontain, or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium and/or data usedthereby may be transmitted using any appropriate medium, including butnot limited to wireless, wireline, optical fiber cable, RF, etc., or anysuitable combination of the foregoing.

Computer program code for carrying out operations for some embodimentsof the present invention may be written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Java, Smalltalk, C++ or the like and conventionalprocedural programming languages, such as the “C” programming languageor similar programming languages. The program code may execute entirelyon the user's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Some embodiments of the present invention may be described below withreference to flowchart illustrations and/or block diagrams of methods,apparatus (systems) and computer program products according toembodiments of the invention. It will be understood that each block ofthe flowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example, and for purposes ofillustrative discussion of embodiments of the invention. In this regard,the description taken with the drawings makes apparent to those skilledin the art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1A schematically represents a catheter probe being brought intocontact with a tissue wall for measurement of a dielectric contactquality therebetween, according to some embodiments of the presentdisclosure;

FIG. 1B is a simplified and schematic plot of contact force anddielectric contact quality as a function of advancement of probe againsttissue wall, according to some embodiments of the present disclosure;

FIG. 1C is a simplified and schematic plot of contact force anddielectric contact quality as a function of time and advancement ofprobe against a cyclically moving tissue wall, according to someembodiments of the present disclosure;

FIG. 1D schematically represents rotation of a catheter probe through arange of contact angles with a tissue wall for measurement of adielectric contact quality therebetween, according to some embodimentsof the present disclosure;

FIG. 1E schematically represents a catheter probe comprising a contactforce sensor, according to some embodiments of the present disclosure;

FIG. 1F is a simplified and schematic plot of contact force anddielectric contact quality as a function of time and angle of probeagainst a cyclically moving tissue wall, according to some embodimentsof the present disclosure;

FIG. 1G schematically illustrates a system for the measurement of tissuedielectric properties, according to some embodiments of the presentdisclosure;

FIG. 2 is a flowchart of a method for the measurement of tissuedielectric properties for determination of contact quality, according tosome embodiments of the present disclosure;

FIG. 3 schematically illustrates a catheter-deployed probe comprising aplurality of electrodes configured for sensing of dielectric contactquality, according to some embodiments of the present disclosure;

FIG. 4 illustrates a graphical user interface (GUI) widget for displayof dielectric contact quality information to a user, according to someembodiments of the present disclosure;

FIG. 5 is a graph presenting estimates of contact force derived fromdielectric contact quality measurements, the estimated contact forcesbeing plotted with respect to directly sensed contact forces, accordingto some embodiments of the present disclosure;

FIG. 6 is a graph of receiver operating characteristic (ROC) presentingfor the data of FIG. 5 a true positive rate versus false positive ratefor dielectric contact quality-based estimation of contact force above athreshold of grams-force, according to some embodiments of the presentdisclosure;

FIG. 7A schematically illustrates a view of a graphical user interface(GUI) widget, representative of the-D orientation of the atria of aheart in space, according to some embodiments of the present disclosure;

FIG. 7B schematically illustrates a heart in an orientationcorresponding to the orientation of GUI widget, according to someembodiments of the present disclosure;

FIG. 7C shows views of six different orientations of GUI widget,separated by about ° from each other, according to some embodiments ofthe present disclosure;

FIG. 7D shows the views of FIG. 7C reduced in size, alongsidecorresponding anatomical views of a heart, according to some embodimentsof the present disclosure;

FIGS. 8A-8E illustrate a display for indicating lesioning status,including contact force, to a user, according to some exemplaryembodiments;

FIG. 9 illustrates display elements which are optionally used toindicate estimated transmurality of a lesion to a user, based on pre-and post-lesioning dielectric property measurements;

FIG. 10 is a graph presenting dielectric property-estimated contactforce vs. directly measured force, according to some exemplaryembodiments of the invention.

FIG. 11A graphs contact force measurements using a force sensingcatheter;

FIG. 11B graphs contact quality level estimates made based on dielectricmeasurements for the epoch also shown in FIG. 11A;

FIG. 11C graphs contact force measurements using a force sensingcatheter; and

FIG. 11D graphs contact quality level estimates made based on dielectricmeasurements for the epoch also shown in FIG. 11C.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to systemsand methods for probe positioning within a body cavity, and moreparticularly, but not exclusively, assessment of contact between anintra-body electrode and a body cavity surface.

Overview

An aspect of some embodiments of the present invention relates toevaluation of contact between an electrode and a tissue surface based onmulti-parameter dielectric property measurements. In some embodiments,the electrode is intra-body (for example, an electrode introduced intothe body over a catheter), and the tissue surface is an internalsurface, for example, the wall of a heart, or of another organ such as alumen of the digestive tract (e.g., the stomach).

In some embodiments, dielectric property measurements include samplingof electrical signals affected by dielectric properties in theenvironment surrounding the intra-body electrode. Movement of theintra-body electrode, and in particular, movement that affects a degreeof contact with an internal surface of a target tissue, changes thisenvironment, leading to changes in measured dielectric properties. Insome embodiments, the evaluated contact is converted to and/or expressedas a dielectric contact quality, for example as a value from along adielectric contact quality scale. For certain applications comprisingtranscatheter delivery of a disease treatment, it is a potentialadvantage to distinguish between different degrees of contact between aprobe which delivers the treatment, and tissue being treated. Degree ofcontact potentially affects treatment results; for example, by affectingthe coupling of energy transfer between a treatment probe and targettissue. For embodiments in which a treatment relies on energy transfer(heating or cooling, for example) “contact quality per se” refers to howthe various physical correlates of degree of contact (e.g., contactsurface area and/or microscopic distances between surfaces approachingone another) influence such coupling. Actual measures of parametersaffected by contact, including, for example, contact force anddielectric contact quality, may in turn be understood as measures ofcontact quality which estimate contact quality per se, and thus also,for example, are optionally used as predictors of a probe-deliveredprocedure's effectiveness.

In some embodiments of the invention, electromagnetic signals indicativeof dielectric properties of an electrode's environment are convertedinto one or more measures of contact quality. In some embodiments, theconversion comprises a mapping from measurements of a plurality ofdielectric properties to a mapped value. Herein, such a dielectricproperty-derived measure of contact quality is referred to as a measureof “dielectric contact quality” (that is, a contact quality which isdielectrically derived). Optionally, dielectric properties aredetermined by analysis of multidimensional signals (e.g. indicative ofimpedance characteristics of tissue nearby (including contacting) asensing electrode. The signals carry information indicative, forexample, of imaginary and/or real components of impedance as a functionof a plurality of electrical field frequencies.

Optionally, these multidimensional signals are converted to a simpler(e.g., lower-dimensional, for example, single-dimensional)representation as a value on a scale of dielectric contact quality. Insome embodiments, dielectric contact quality is expressed as a categoryexpressing a character of contact (sufficient, insufficient, and/orexcessive contact, for example), and/or as a numerical value whichcharacterizes contact, the characterizing value being with or withoutunits (e.g., 20%, 10 grams-force, a scale of integers, etc.). In someembodiments, at least four different levels of dielectric contactquality are identified. Optionally, at least two levels of sufficientcontact (sufficient for performance of an ablation or other procedure,for example) are distinguished. In some current practice, contact force(as measured, for example, by a piezoelectric force sensor) is used as astandard for estimating a contact quality per se. In some embodiments ofthe present invention, a quality of contact is expressed as a contactforce equivalent. For example, a certain contact quality is optionallyexpressed in units of gram-force which correlate with units ofgram-force actually exerted by the contact, even though the actualmeasurement is optionally by the analysis of signals which are not ofcontact force.

Use of contact force measured by an ablation probe force sensor has beenintroduced in the prior art for ablation treatment (by RF ablation, forexample) of atrial fibrillation (AF). Ablation performed in thistreatment approach seeks to abolish atrial fibrillation by cutting (atthe point of ablation) conduction pathways leading between regions ofimpulse initiation and contractile myocardial tissue. For example,ablation is optionally performed to cut off sites of electrical impulsegeneration in or near the pulmonary veins (PV) from the rest of theheart.

AF can recur, for example, in about 50% of patients after ablation, withthe majority of recurrences (about 95%, for example) being associatedwith the restoration of a conductive pathway leading from a pulmonaryvein (PV reconnection). Use of contact force measurement to guideablation has led to an apparent reduction in PV reconnection.Nevertheless, it has been observed that the efficacies of somealternative ‘cut and sew’ (Cox-MAZE) methods of interrupting conductionpathways continue to exceed that of catheter-based AF ablation, evenusing contact force as a guide. Moreover, current methods of contactforce measurement rely on specialized probes comprising a force sensor.

Dielectric contact quality offers some potential advantages over contactforce as an estimator of contact quality per se. For example, theimpedance of an electrical circuit comprising tissue near the contactbetween the probe and the tissue may be indicative of electromagneticcoupling affecting the transfer of ablation energy between a probe andtissue. As a measure of electromagnetic coupling, contact forcemeasurement is potentially a more indirect indication than dielectriccontact quality. Also for example, it is a potential advantage fordirectness of measurement to use the same electrode for both contactsensing and ablation (this is possible, for example, when using RFablation). Furthermore, it is a potential advantage to be able to obtaina measure of contact quality using a probe that lacks a specialadditional force sensor. In some embodiments, a multi-electrode probe isprovided; e.g., a probe comprising a plurality of electrodes arrangedalong a longitudinal extent of the probe. Optionally, the electrodes arearranged on the probe (for example, the probe may be flexible) so thatthey can be brought into simultaneous contact with a tissue surface. Insome embodiments, each of the plurality of electrodes is separatelyoperable for determination of a corresponding dielectric contactquality. This is a potential advantage for multi-electrode applications,since it may be prohibitively difficult to provide each electrode withits own corresponding force sensor.

An aspect of some embodiments of the present invention relates to therepresentation of dielectrically measured contact quality between anelectrode and a tissue surface as a force-unit equivalent. In someembodiments, a displayed indication of dielectric contact quality ispresented to a user as an estimated equivalent value in units of force.This is a potential advantage for allowing dielectric contact qualityresults to be referenced to a device-independent standard. For example,tissue contact guidelines in a protocol for treatment (e.g., tissueablation) are optionally provided in terms of a unit of force such asgrams-force, Newtons, millinewtons, or another standard unit.

In some embodiments, a calibration scale allowing the translation formdielectric contact quality to contact force is obtained from trainingtrials in which contact force is directly observed in conjunction withdielectric contact quality measurement. In some embodiments, a displayof dielectric contact quality comprises two or more complementarydisplays; for example, a graphical bar display allowing at-a-glance(optionally, peripherally viewed) judgment of general contact status,together with one or more numeric indications suitable to directcomparison with protocol guidelines.

An aspect of some embodiments of the present disclosure relates to theuse of a graphical user interface (GUI) widget for representation of anorgan orientation in a 3-D space. In some embodiments, the organ is aheart, or portion of heart anatomy, for example, atria of a heart.

In some embodiments, a mutable 3-D view of an organ's anatomy ispresented to a user for use in tasks such as procedure planning, probenavigation and/or probe positioning. The 3-D view is optionally mutablein one or more of a numerous respects including not only orientation,but also (for example) color, completeness, texture, transparency,and/or scale. This mutability provides a potential advantage for richvisual presentation of information. For example, regions of interest canbe magnified for detailed work; color mappings are optionally used torepresent physiological parameters such as tissue vitality and/orthickness. However, mutable display also creates a risk of cognitiveoverload which potentially leads to operator disorientation,distraction, and/or fatigue. A sense of spatial orientation inparticular can be difficult to continually maintain, yet awareness oforientation is potentially crucial to the success of a procedurecomprising navigation of a catheter probe through complex and/orconstraining anatomical structures.

In some embodiments, a GUI widget representative of the features of anorgan is provided for coordinated display with a 3-D view of an organ'sanatomy. The coordination, in some embodiments, comprises coordinatedadjustment of the orientation of the GUI widget to the orientation ofthe anatomical view, such that knowing the orientation of the GUI widgetuniquely determines the 3-D orientation of the anatomical view. The GUIwidget is optionally manipulated by user input directed at the GUIwidget itself, and/or updated to reflect user input directed at anothercontrol (for example, sliders, buttons, and/or the anatomical viewdisplay itself).

Optionally, the GUI widget is comprised of simple geometrical shapeswhich suggest (without literally depicting) anatomical landmarks of thetrue anatomy. Optionally, the landmarks which are shown are those mostsalient to treatment and/or diagnostic activities that the anatomicaldisplay is supporting. For example, blood vessels which mark navigationpathways and/or treatment zones are optionally shown as cylindricaltubes. Complex shapes (such as the atria and valves) are optionallyreduced to a small number of salient visual indications, such asposition and/or relative size. GUI widget representation of anatomicalstructures peripheral to an operator's activities (for example, theventricles) are optionally suppressed altogether. Such a GUI widgetprovides a potential advantage in striking a balance between twoopposing constraints: being visually stable and simple enough thatorientation is instantly identifiable to a device operator, yet beingenough similar to actual anatomy that orientation homology is directlyapparent.

Optionally, one or more indications of anatomical structures separatefrom the displayed anatomy are provided for indication of orientation.For example, a cylinder showing the relative position of the esophagus(which can potentially be at risk for damage during ablation) isoptionally displayed near a schematic model of the atria. In someembodiments, a portion of a lumen of the digestive tract (e.g., astomach) is schematically represented. Optionally, orientation isindicated by cylinders representing entrance and exit passages from therepresented tissue. Optionally, orientation is indicated by a schematicrepresentation of the position of a characteristic bend of a lumenalstructure, for example: a bend of a large intestine or an arch of anaorta.

In some embodiments, a GUI widget is adjustable in one or morecharacteristics additional to orientation. For example, view scale isoptionally indicated by marking of anatomical view regions on the GUIwidget. Optionally, internal anatomy views (as is from within an atriumfor example) are distinguished from external anatomy views. This isperformed, for example, by visually cutting away a portion of the GUIwidget so that its modeled interior is seen.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings. The invention is capable of otherembodiments or of being practiced or carried out in various ways.

Dielectric Contact Quality

Reference is now made to FIG. 1A, which schematically represents acatheter probe 111 being brought into contact with a tissue wall 50 formeasurement of a dielectric contact quality therebetween, according tosome embodiments of the present disclosure. Reference is also made toFIG. 3, which schematically illustrates a catheter-deployedmulti-electrode probe 112 comprising a plurality of electrodes 103configured for sensing of dielectric contact quality, according to someexemplary embodiments of the present disclosure.

In some embodiments, at least one electrode 103 of a catheter probe 111,112 is configured for use in producing a time-varying electrical field104 across tissue wall 50 (a second electrode used in field productionnot shown), while the probe 111, 112 approaches and is forced intocontact with a tissue contact region 106. In some embodiments, eachindividual electrode 103 of multi-electrode probe 112 optionallyseparately defines a tissue contact region 106. Electrodes 103 ofmulti-electrode probe 112 are optionally operated to produce anelectrical field between pairs of electrodes 103, and/or between anelectrode 103 and an electrode positioned remotely. Electrode 103 isalso configured for the measurement of signals from the time-varyingelectrical field 104 which reflect the dielectric properties of theelectrode's environment. In some embodiments, these signals change asthe probe 111 is moved through a distance 61, for example, from position111A to position 111B. In particular, signals received potentiallychange significantly during movement between an initial contact of probe111 with tissue contact region 106, and a later contact wherein probe111 has been further forced against tissue contact region 106.

Herein, tissue ablation from a probe provides an example of aprobe-delivered, contact quality-dependent procedure. It is to beunderstood that other probe contact quality-dependent procedures arealso included within the scope of this disclosure; for example, contactas a preliminary to biopsy sampling.

In some embodiments, probe 111 (optionally electrode 103 itself) isadapted for use to ablate tissue at contact region 106. The outcome ofsuch ablation, and in particular RF ablation, has been found tosignificantly depend on how contact is formed between the ablation probeand the tissue. Optionally, for example, a degree of contact couplingbetween an ablation probe and target tissue affects how energy istransferred between them to produce ablation. Dielectric assessment ofcontact also provides a potential advantage in evaluation of dataapplicable to other dielectric measurement modalities. For example, thevalidity of dielectric tissue state assessment (e.g., lesion extentand/or continuity, tissue edema) is optionally verified at least in partby confirmation of a minimum quality of contact by the electrode usedfor measurement.

In some embodiments, other electrodes, another catheter probe and/oranother ablation method is used in a procedure, for example,cryoablation, ultrasound ablation, laser ablation, electroporatingablation, or another form of ablation. In such instances, coupling ofcontact quality sensed by electrode 103 to effective contact by theportion of the probe comprising an element which is actuated to performa treatment procedure is optionally obtained, for example, by puttingboth electrode 103 and the treatment element on the same probe.Optionally, the contact sensing electrode and the procedureadministrating portion (e.g., lesioning element) of the probe arepositioned, for example, alongside each other, encircling one another,and/or interpenetrating one another at a contact surface. Additionallyor alternatively, a contact offset between the two probe elements isaccounted for in calibration. In some embodiments, a plurality of probes(e.g., one carrying the contact sensing electrode, and one carrying theprocedure administrating portion) are positioned in tandem so that asensed dielectric contact quality from a first probe provides usefulinformation about the contact quality of a second probe.

In some embodiments, a plurality of electrodes 103 on a multi-electrodeprobe 112 used in sensing of dielectric contact quality are optionallyoperable for treatment (e.g., lesioning) and/or assessment of treatmentresult (dielectric assessment of treatment results, e.g., lesioncharacteristics, is described, for example, in U.S. Provisional PatentApplication No. 62/291,065 to the applicant, the contents of which areincorporated herein by reference in their entirety. For example, probe112 is optionally flexible (e.g., into a loop shape as shown in FIG. 3)to assume the shape of a portion of an extended train of tissue lesionfoci, allowing electrodes 103 to be positioned therealong. Assessment ofcontact quality for each electrode provides a potential advantage byallowing the selective operation of electrodes in good contact forablation and/or dielectric tissue assessment, reducing the potential forineffective treatment and/or spurious results due to lack of qualitycontact at one or more of the electrode positions.

In some embodiments, evaluation of contact quality comprisescategorization of contact quality. For example, a distinction is madebetween contact which is sufficient for successful ablation, and contactwhich is insufficient. In some embodiments, contact force large enoughto create a potential risk of tissue perforation is distinguished asanother category. Optionally, contact quality comprises a quantitativeevaluation; for example, ordered (optionally, continuous) gradationsbetween and/or within each category of contact.

In some embodiments of the invention, signals and/or their changesindicative of dielectric properties of the environment of electrode 103are converted into one or more measures of contact quality. Theconversion optionally involves dimensional reduction of the inputs fromwhich contact quality is derived.

For example, impedance measurements used as inputs of this conversionare optionally multidimensional (impedance measurements are used, insome embodiments, as indications of dielectric properties). An impedancemeasurement may comprise an impedance value for each of a plurality offrequencies. Each impedance value may have a real part and/or animaginary part, which may be considered a dimension of the input.

Parameters that affect signals indicative of dielectric properties mayinclude, for example, not only contact quality, but also aspects ofother elements of the contact quality measurement circuit, for example:

-   -   The configuration of circuit elements including the probe 111        and/or electrode 103 itself;    -   The dielectric properties of tissue including tissue wall 50,        tissue contact region 106, and/or other tissue (such as body        tissue 102 of FIG. 1G) in which electrical field 104 is        established; and    -   The configuration of other circuit elements, for example, skin        patches 105 (FIG. 1G), leads, and other electrical components of        a dielectric measurement system.

Nevertheless, the inventors have surprisingly found it possible todetermine a correspondence (by correlation, for example) betweenmultidimensional dielectric measurements and one or more other measuresof contact quality. Insofar as force-measuring probes are currentlyavailable and in use, contact force measurement provides a preferredexample of a reference against which calibration of dielectric contactquality is optionally performed. However, estimation of contact qualitybased on dielectric measurements is not limited to comparisons withcontact force measurements. For example, results of dielectricmeasurements may be correlated with (or calibrated against) directmeasurements of procedure results (e.g., ablation effectiveness).Optionally, a measure of contact quality comprises a combined assessmentof dielectric contact quality and contact force as measured by aforce-sensing probe. For example, optionally, an anticipated procedureresult is jointly predicted by sensed force and dielectric contactquality.

In some embodiments of the current invention, there is a correspondencedetermined between dielectric measurements, and the force with which aprobe 111 bearing an electrode 103 is pushed into a tissue contactregion 106. Herein, such a determined correspondence is called a scaleof dielectric contact quality. Contact force can be directly measured,for example, from the deformation of a piezoelectric device mounted to aspecialized force-measuring catheter probe.

Optionally, correspondence is determined by means of a calibrationprocedure. The calibration procedure comprises, for example,simultaneously measuring both dielectric properties and contact forcesin a number of calibration experiments (for example, 100, 1000, 10000,or another larger or intermediate number of calibration experiments).Optionally, calibration experiments are performed with an ex vivopreparation of the target tissue of interest; for example, a preparationof myocardial tissue when dielectric contact quality with heart walltissue is to be determined. Additionally or alternatively, calibrationcomprises measuring dielectric properties from a probe during aprocedure and corresponding experimental and/or actual procedure results(for example, ablation lesion results). From these data, a dielectriccontact quality scale is determined in some embodiments; for example, byuse of statistical analysis, machine learning, and/or another techniquefor extracting associations from multivariate data. In some embodiments,further information is used; for example, anatomical data (e.g., generalatlas data, and/or data personalized to the patient) and/or probeposition data. Optionally, this further information serves to affect howa scale is applied, for example, by providing values of parametersaffecting dielectric contact quality determination. Optionally,relationships established by the calibration procedure are provided asdata structure 130 of a contact quality assessing system 100, forexample, as described in relation to FIG. 1G. Optionally, data structure130 comprises a mapping between a plurality of dielectric measurementresults, and a corresponding plurality of values along a contact qualityscale. The contact quality scale is optionally one dimensional.Optionally the scale is expressed in units equivalent to force.Additionally or alternatively, it is expressed in terms of an arbitraryunit (for example, a one or two digit value on a relative scale).

In some embodiments, a contact quality assessing system 100 includescalibration data (for example, data structure 130) for a plurality ofdifferent probe 111 and/or electrode 103 types. The calibration data foruse is optionally selected based upon identification of the probe 111and/or electrode 103 type. In some embodiments a probe 111 and/orelectrode 103 is provided together with calibration data (for example,data structure 130) which can be in turn provided to contact qualityassessing system 100 for use. Optionally, the calibration data isindividualized to the provided probe 111 and/or electrode 103. In someembodiments, a calibration phantom is provided which allows at leastpartial recalibration of probe 111 and/or contact electrode 103. Forexample, the calibration phantom optionally comprises a mount for probe111, and a force sensor which measures the force with which electrode103 presses against a phantom tissue which is part of the calibrationphantom (for example, a fluid-filled bag, a polymer membrane, and/oranother artificial substitute for contacted tissue). Optionally, forceand/or dielectric property measurements made using the calibrationphantom are used as indications to adjust use of data structure 130 sothat contact quality assessments are calibrated for the particularconfiguration of the contact quality assessing system 100.

Reference is now made to FIG. 1B, which is a simplified and schematicplot of contact force and dielectric contact quality as a function ofadvancement of probe 111 against tissue wall 50, according to someembodiments of the present disclosure.

Arrow 61 represents the motion 61 of FIG. 1A. Dotted line 65A representsa direct force generated between the probe 111 and the tissue contactregion 106. Initially (e.g., up to inflection point 65B), this force issubstantially zero. It begins to rise on initial contact, and continuesto rise until the end of the graph. The rise of force as a function ofdistance is simplified to a linear relationship for purposes ofillustration. Also in the example of FIG. 1B, and during the sameadvancement of probe 111 into tissue, dielectric measurements areoptionally taken. Solid line 66A represents the evolution of a measureof contact quality which these dielectric measurements comprise (theconversion being performed, for example, as determined by a previouscalibration procedure).

While the two measures (e.g., of direct contact force and of dielectriccontact quality) are not necessarily linearly related throughout thecalibration range, there are, in some embodiments, three regions inparticular which can be assigned a qualitative functional significance.Region 62 of FIG. 1B is a low-contact region of the graph, optionallydefined as a region of the graph within which there is an elevated riskof failure for a procedure (an ablation procedure, for example)performed at that level of contact. Region 64 is an excessive-contactregion of the graph, optionally defined as a region of the graph withinwhich there is an elevated risk of perforation by probe 111, and/orother mechanical trauma. Region 63 represents an intermediate region ofcontact quality within which procedure success (ablation proceduresuccess, for example) is predicted.

As represented, the relationship between contact force and contactquality is approximately linear in the predicted success range 63 (anon-linear relationship is also possible). Optionally, there are largerdeviations from linearity in range 64 and/or range 62. This is shownalso in the data-derived example of actual vs. estimated contact forceof FIG. 5. The deviation (apparent loss of sensitivity, for example) isnot necessarily a practical limitation of the dielectric method: theextreme ranges anyway are optionally considered as “avoided regions” forpurposes of treatment. Moreover, it should be understood that contactforce, though optionally used as a reference standard (for example, as aguide in actual clinical practice), itself is a proxy for contactquality per se as defined hereinabove. Potentially, dielectric contactquality is a predictor of procedure results comparable to, or evenbetter than contact force.

Reference is now made to FIG. 1C, which is a simplified and schematicplot of contact force and dielectric contact quality as a function oftime and advancement of probe 111 against a cyclically moving tissuewall 50, according to some embodiments of the present disclosure.

The features of FIG. 1C are generally the same as for FIG. 1B, with theexception that a cyclical motion 51 of tissue wall 50 has beenintroduced. This is a typical situation, for example, when applying aprobe to a heart wall. In some embodiment of the invention, dielectriccontact quality is measured as part of a tissue ablation procedure bymeans of an ablation probe applied to a heart wall (an atrial wall, forexample). Physiological motion (for example, the beating of the heartand/or respiration) potentially produces time-varying contact quality(indicated, for example, by range 51A). Plots of both contact force 65and dielectric contact quality 66 are shown. Plot 66B shows amotion-corrected contact quality force-equivalent, for reference.Optionally, a dielectric contact quality scale is reported as theinstantaneous contact quality. Additionally or alternatively, in someembodiments, dielectric contact quality is corrected for motion, forexample, by time averaging, filtering, or another signal processingmethod.

Moreover, in some embodiments, a scale of dielectric contact qualityoptionally takes physiological motions into account as being themselvesindicative of contact quality. In the example shown, large changes occurwithin the range of acceptable contact, while changes are smaller ascontact is initiated, and/or as contact becomes excessive. It is to beunderstood, however, that the actual relationship between impedanceswings and contact quality may be different, according to what isobserved in calibrating a scale of dielectric contact quality for aparticular probe, tissue, and/or procedure.

Reference is now made to FIG. 1D, which schematically representsrotation of a catheter probe 111 through a range of contact angles 67with a tissue wall 50 for measurement of a dielectric contact qualitytherebetween, according to some embodiments of the present disclosure.Reference is also made to FIG. 1E, which schematically represents acatheter probe 111 comprising a contact force sensor 71, according tosome embodiments of the present disclosure.

In some embodiments, contact of probe 111 with a tissue contact region106 comprises contact at an electrode 103 which is shaped (for example,rounded) to present a substantially similar contact geometry through awide range of contact angles 67 as it moves between a first position111C and a second position 111D. For a given resulting force applied byprobe 111 in a direction orthogonal to tissue wall 50, it can beunderstood that the resulting contact surface area (and so, to a closeapproximation, the contact quality of that contact) should be the samein all positions. However, the determination of the forces experiencedby the probe along these directions is potentially prone to error from asingle-direction contact force sensor 71. If force sensor 71 is alignedto sense force along direction 70, for example, then it will potentiallyonly sense the component of contact force 72 which is aligned withdirection 70. At least a portion of the component of contact force 72aligned with direction 69 is potentially unobserved, leading to contactangle dependence for force sensed by contact force sensor 71. Additionof one or more additional sensors (for example, to sense lateral forces)can raise engineering difficulties, since the catheter probe 111 itselfis likely to be highly constrained in diameter (leaving little room forextra wiring, or even for the extra sensor itself).

In some embodiments, dielectric contact quality estimation issubstantially constant (for example, constant within about 5%, 10%, 15%,or another smaller or intermediate value) while contact angle 67 iswithin 30° of a central angle of contact; for example, a central angleof contact comprising orthogonal positioning of probe 111 to tissue wall50. Optionally, the angular range of substantially constant dielectriccontact quality estimation is within 45°, 60°, 75°, or another larger,smaller, or intermediate angle from the central angle of contact.

Reference is now made to FIG. 1F, which is a simplified and schematicplot of contact force and dielectric contact quality as a function oftime and angle of probe 111 against a cyclically moving tissue wall 50,according to some embodiments of the present disclosure.

Contact force/quality traces 65, 66, and 68 are shown as a function oftime and angle of probe with a tissue contact region 106, the anglechanging in the direction of arrow 67 (shown as an arc in FIG. 1D).Cyclical motion of tissue wall 50 is also included in the traces. Trace65 represents an actual contact force orthogonal to tissue wall 50,while trace 68 represents a contact force estimated from a contact forcesensor 71 aligned to sense force exerted along the longitudinal extentof probe 111. As shown in the example, the sensed force increasingunderestimates the true force as the contact angle deviates from truevertical, indicated by mark 73.

A potential advantage of dielectric contact quality measurement, in someembodiments, is that the resulting scale (measurements shown asdielectric contact quality trace 66) is optionally independent ofcontact angle. Optionally, this is a natural consequence of themeasurement, particularly if the geometry of the contact surface is whatdominates the impedance measurements. Additionally or alternatively,even if impedance itself has some angular dependence for a particularelectrode configuration, the scale by which it is converted to a measureof dielectric contact quality may be calibrated to compensate. Thisoption arises, for example, if there are one or more parameters of themulti-parameter impedance measurement which sufficiently correlate withcontact angle.

System for Measurement of Dielectric Properties

Reference is now made to FIG. 1G, which schematically illustrates asystem 100 for the measurement of tissue dielectric properties,according to some exemplary embodiments of the present disclosure.

In some embodiments, dielectric properties of tissue are assessed fordetermining a quality of contact (dielectric contact quality) between anelectrode and tissue. Optionally, the dielectric contact quality isused, for example, in the planning and/or creation of tissue lesions. Insome embodiments, tissue lesions are made for treatment, for example, ofatrial fibrillation, hypertrophic obstructive cardiomyopathy,neuromodulation, and/or tumors. Dielectric property measurements aremade, for example, based on the frequency- and/or time-dependentresponse characteristics of an electrical circuit comprising a targettissue. In some embodiments, circuit response characteristics compriseoutput signals (e.g. changes in voltage potential) in response to one ormore input signals (e.g., driving frequencies).

In some embodiments, system 100 comprises an electrical fieldmeasurement device 101B, connected to a set of catheter electrodes 103,and a set of skin-patch electrodes 105 to measure properties (forexample, voltage potential and how it changes) of time-varyingelectrical field 104 therebetween. In some embodiments, electrical fieldmeasurement device 101B comprises a power meter (e.g., an RF powermeter), a volt meter, and/or an ampere meter, configured to measurepower, voltage, and/or current sensed by catheter electrode 103. Themeasured electrical field is generated by a field generator 101A;optionally included together in a combined electrical fieldgeneration/measurement device 101. In some embodiments, a catheter probe111 comprising the catheter electrodes 103 is introduced to the regionof a tissue to be ablated by means of a catheter 109. In someembodiments, the skin patch electrodes 105 are externally applied, forexample, to the body of a patient. In operation of system 100, field 104is induced in tissue 102 (for example, tissue of a patient's body)separating the catheter electrodes 103 and the skin patch electrodes105. Optionally, the electrical field also extends through a targettissue region 106. Optionally, dielectric contact quality with targetregion 106 is assessed as part of guiding treatment administered throughprobe 111, for example, treatment by ablation (lesion formation).

As described, for example, in relation to FIG. 2, measurements offrequency-dependent impedance in the electrical circuit(s) resultingfrom this configuration reflect electrical properties of tissue throughwhich the electrical field extends (in particular, dielectricproperties). The dielectric properties sensed change according to theenvironment of electrode 103, and in particular, according to a degreeof contact with target region 106.

Optionally, the number of catheter electrodes is 2, 3, or 4 electrodes.Optionally, a greater or lesser number of catheter electrodes is used.Optionally, the number of skin patch electrodes is 4, 5, or 6electrodes. Optionally, a greater or lesser number of skin patchelectrodes is used.

Optionally, the characteristics of the time-varying electrical field 104are chosen to be appropriate to a measurement function which is to beperformed. Typically (for measurement functions), the frequencies of theelectrical field used are in the range of 10 kHz to 13 kHz. In someembodiments, the frequencies of the electrical field used formeasurement are in a range, for example, of about 8 kHz-15 kHz, 5 kHz-20kHz, 10 kHz-25 kHz, or another range having the same, larger, smaller,and/or intermediate bounds.

Optionally, the number of frequencies used is 10 or fewer frequencies.Optionally, the frequencies are distributed evenly throughout the fullrange of frequencies chosen. Optionally, frequencies chosen areconcentrated in some particular frequency range. Applied voltages arepreferably in the safe range for use in humans, for example, 100-500millivolts, and/or a current of 1 milliamp or less (a typical bodyresistance is about 100 0). Resulting field strengths are in the range,for example of a few millivolts per centimeter; for example, 5 mV/cm, 10mV/cm, 20 mV/cm, or another larger, smaller, or intermediate value.Based on requirements for data acquisition, sensing time is optionallyabout 10 msec per measurement (or a longer or shorter period, forexample, about 100 msec, or 1 second), for embodiments including fastautomated switching of frequencies and/or electrode pairs.

In some embodiments, a method of correlation (for example, as describedin relation to calibrating the device of FIG. 1A, herein) is optionallyused to relate measured electrical properties (dielectric-relatedproperties in particular) of tissue as a function of a degree of contacttherewith to procedure results (e.g., lesioning effectiveness), and/orto another measure of contact quality such as contact force. It can beunderstood that any sufficiently dense sampling of frequencies may beinitially measured with respect to a particular system and set of tissueconditions to determine which frequencies show the most useful results.The reduction to a number practical for online use can be based on whichfrequencies yield data having the greatest statistical correlation withresults. It has been found by the inventors that ten or fewerfrequencies, distributed, for example, within the range of 10 kHz to 13kHz, are useful to allow contact assessment. It should be noted thatpublished permittivity and conductivity values of many tissues,including heart, are roughly linear in log: log plots over ranges of afew hundred kHz within the range mentioned, which potentially allowsdistinctions among tissue types to be made without a requirement fordense frequency sampling.

In some embodiments, catheter probe 111 is optionally used for ablationby RF ablation energies delivered through the catheter electrodes 103which are also used for measurements. Optionally, catheter electrodes103 are provided as part of a standard catheter probe, operated with asystem capable of driving, sensing and/or analyzing circuits so as toacquire data suitable for dielectric property analysis.

In some embodiments, other electrodes, another catheter probe and/oranother ablation method is used, for example, cryoablation, ultrasoundablation, laser ablation, electroporating ablation, or another form ofablation.

In some embodiments, the electrical field generation and/or electricalfield measurement device 101A, 101B is under the control of controller120, which itself is optionally under user control through userinterface 150. Controller 120 optionally comprises a computer with CPUor other digital hardware operating according to programmed code.Controller 120 is described herein as a multi-functional module;however, it is to be understood that functions of controller 120 areoptionally distributed among two or more modules of the system.

Electrical field generation by device 101; for example, to probedielectric properties of the tissue environment by means of impedancemeasurements, is under the control of controller 120. Measurements fromdevice 101, for example, of impedance parameters used in measuringdielectric properties, are communicated back to the controller 120,and/or a measurement module 120A. In some embodiments, controller 120also comprises an ablation controller (not shown). Ablation isoptionally via electrical fields (e.g., RF electrical fields) generatedby device 101, or by another ablation method, for example as describedherein.

In some embodiments, controller 120 comprises contact characterizationmodule 120B, relating measurements to one or more additional parametersto produce a measure of dielectric contact quality. For example, stateinputs provided at 140 optionally comprise any state relevant to themeasurements, including, for example, details of the anatomy of tissue102 and/or target region 106. Optionally, position inputs 135 areprovided to define position(s) of catheter electrode 103 and/or skinpatch electrodes 105 relative to anatomy.

In some embodiments, details of anatomy comprise image data givingtissue types in positions through which field 104 is induced.Optionally, details of anatomy comprise a dielectric property model ofthe anatomy, for example, dielectric properties inferred from image dataand/or typical dielectric properties of different tissue types.Optionally, the model is refined by additional data received byelectrode sensing, for example, sensing from catheter electrodes 103 andskin patch electrodes 105. In some embodiments, user interface 150 isprovided with means for governing how controller 120 uses availablestate inputs 140 and/or position inputs 135—for example, to reviewand/or correct data-to-model registration, adjust model parameters, andthe like. Optionally, system 100 comprises correlation data structure130, functionally connected with controller 120. In some embodiments,the correlation data structure comprises data by which measuredelectrical field properties (in particular, those associated withdielectric properties of target tissue) are linked to dielectric contactquality. The linkage is optionally (for example) by statisticalcorrelation, by use of a machine learning result, and/or by use ofequations fit to correlation data. In some embodiments, correlations aresupplemented by modeling of the effects of one or more physicalproperties: for example, temperature, and/or time-varying filling withfluid (such as blood) and/or gas (such as air). In some embodiments, thedata structure is compiled by the application of one or more of suchlinkage methods to previously recorded calibration data. For example,calibration lesions are formed, and separate measurement of dielectricproperties and corresponding lesion sizes (and/or other lesion stateinformation, such as lesion type and/or condition) are performed. Insome embodiments, contact force is measured along with measurements fordielectric contact quality, and correlation data structure 130 is builtbased on correlations between these two measures. Optionally, additionaldata, for example, state data such as is provided by state inputs 140,is also measured.

In some embodiments, the relationships among measurements are stored incorrelation data structure 130 in such a way that a vector of dielectricproperties from field generator/measurement device 101, optionallysupplemented by information from state inputs 140, can be used toestimate dielectric contact quality (optionally, contact qualityexpressed as contact force). In some embodiments, correlation datastructure 130 also comprises information relating to other tissueproperties, for example, properties of an existing, targeted, ordeveloping lesion. Lesion properties include, for example, lesion size(e.g., lesion depth, width, and/or volume), and/or type or condition(e.g., reversible, irreversible, transmural, fibrotic, and/oredematous). In some embodiments, dielectric contact quality iscontinuously variable, for example, expressed in arbitrary units, or inforce-equivalent units. In some embodiments, dielectric contact qualitycomprises a category assignment—for example, contact is estimated asbeing within one of a plurality of contact quality categories (e.g.“insufficient”, “sufficient”, or “excessive” with respect to one or morecriteria of a procedure such as a lesioning procedure). Optionally, animpedance contact quality assessment is associated with an estimate oflikelihood; for example, a standard deviation and/or a confidence level.

Measurement of Dielectric Properties

Reference is now made to FIG. 2, which is a flowchart of a method forthe measurement of tissue dielectric properties for determination ofcontact quality, according to some exemplary embodiments of the presentdisclosure. Before stepping through the blocks of FIG. 2 in detail,there is now provided a brief overview of impedance measurement. Todescribe a basic measurement of impedance, the following notation isused:

W—A set of frequencies.

C—A set of catheter electrodes.

P—A set of patch electrodes.

Parameters and/or values for each of the above are, for example, asdescribed in relation to FIG. 1G.

Impedance measurements are optionally expressed as:Z(t)={Z_(w,c,p)(t)|w∈W, c∈, p∈P} where Z(t) is the complex impedance(resistance and reactance) measured at time t and frequency w between acatheter electrode c and a patch electrode p.

Correlation information from any single electrode pair and/or frequencyis generally not a sufficient basis on which to draw conclusions. It isa potential advantage to have numerous vector components (for example,measurements at multiple frequencies between multiple electrode pairs)in order to extract sufficiently strong correlations to allow dielectriccontact quality assessment. Optionally, the number of catheterelectrodes is 2, 3, or 4 electrodes, or a greater or lesser number ofcatheter electrodes. Optionally, the number of skin patch electrodes is4, 5, or 6 electrodes, or a greater or lesser number of skin patchelectrodes. Optionally, 2-10 electrical field frequencies are used, or agreater number of frequencies.

Herein, determination and application of correlations is described interms of vectors, for convenience of presentation. It should beunderstood that in some embodiments, correlations are additionally oralternatively expressed in another form.

In some embodiments, multivariate nonlinear regression and/orclassification analysis is used to establish correlations and/ormappings between measurements (and/or intervals of measurements obtainedas a time series) and one or more of contact quality and contact force.Optionally, correlation and/or mapping is derived from use of a machinelearning technique; for example: one or more implementations of decisiontree learning, association rule learning, an artificial neural network,inductive logic programming, a support vector machine, cluster analysis,Bayesian networks, reinforcement learning, representation learning,similarity and metric learning, and/or another technique taken from theart of machine learning. Optionally, the choice of technique influencesthe storage, expression, and/or retrieval of correlation data. Forexample, correlations are optionally established and/or read-out by useof a machine learning paradigm expressed as an artificial neural networkexpressed in terms of connected nodes and connection weights. In someembodiments, determined correlations are expressed in terms ofassociative rules; for example, one or more functions (optionally fittedto the calibration data) and/or lookup tables.

In some embodiments, determined correlations are expressed in terms ofassociative rules; for example, one or more functions fitted to thecalibration data. In some embodiments, correlations are expressed interms of one or more dielectric measurement profiles. For example,occurrence of a certain degree of contact (e.g., as measured by a forcesensor) is observed during calibration to correlate with one or moreimpedance measurements occurring within one or more correspondingranges. These ranges are optionally established as a dielectric propertyprofile that serves as an indication of the corresponding degree ofcontact when it is observed. Alternatively or additionally tocalibration with reference to another measure of contact quality,impedance contact quality measurements are correlated with the effectsof carrying out a procedure (such as ablation) when a certain impedancecontact quality is obtained. It should be noted that this latterprocedure potentially tends to conflate non-contact parameters affectingdielectric measurement into results unless calibration also accounts forat least one variable which is contact-related (even if not describingcontact itself), such as a distance of electrode advance against atarget tissue.

Use of multiple field measurements potentially assists in the isolationof correlations between field measurements and dielectric contactquality. For example, it can be considered that a substantially commontissue region near (and, in particular, contacting at least one of) eachcatheter electrode c_(i) contributes to the impedance Z_(w,c,p)(t)measured between each pair of electrodes (c_(i), (p₁, . . . p_(m))).This common region potentially increases correlation in impedancemeasurements made between each of those electrode pairs. Conversely, theimpedance contributions of tissue more distant from the electrode probe,separating the electrode probe and any given patch electrode p_(j) arepotentially encoded in correlations between each of the pairs ((c₁, . .. c_(n)), p_(j)).

Even though the impedance interactions of the different tissues(near-catheter and far-from-catheter) are potentially non-linear intheir combined effects on measurements, it can be understood based onthe foregoing how contributions of local and distant tissue arepotentially separable from one another based on correlation properties.

Different tissues have different dielectric properties, providing onebasis on which increasing contact with a tissue can have an effect onthose properties. An electrode within a heart, for example, ispotentially in contact with both blood and a wall myocardial tissue tovarying degrees as an impudence contact quality with the myocardialtissue changes. Published values of dielectric properties in differenttissue types show that blood and cardiac muscle, for example, comprisetwo potentially distinguishable tissue environment components. Featuresof tissue and tissue environments such as blood which affect dielectricproperties (e.g. components of impedance) potentially include, forexample, cellular organization, fibrous organization, and/or thepresence of free fluid and/or the make-up of free fluid constituents.

Referring now to FIG. 2, prior preparation of a subject is presumed tohave been performed before entry into the flowchart at block 250. Insome embodiments, skin patch electrodes are positioned on the body of apatient, in good electrical contact therewith. Optionally, the patchelectrodes are, for example, about 5-15 cm across. Optionally, 3-5 skinpatch electrodes are used, e.g., 3 electrodes.

At block 250, in some embodiments, catheter electrodes are brought intoposition, for example, by navigation through a catheter to a tissueregion (for example, left atrium) at which lesions exist and/or are tobe created. Optionally, at block 251, the position is determined (e.g.,from co-ordinates provided by catheter navigation system), and convertedto position inputs 135 for later use as will be described in relation toblock 254.

At block 252, in some embodiments, fields of selected frequencies areapplied between catheter electrodes C and skin patch electrodes P toobtain measurements of impedance. Measurements of field 104 (for exampleby field measurement device 101B) allow determination of acharacteristic impedance at each frequency, and for each electrodeselection, which produce the set of impedance measurements Z(t).

At block 254, an impedance contact quality determination is made.Determination of dielectric contact quality optionally comprisesinterpretation in view of a current environment (e.g., rough position ina body) of catheter electrodes C, as provided, for example, by positioninputs 135 and/or state inputs 140. In some embodiments, time history ofstate inputs is taken into account; for example, oscillations as afunction of heartbeat and/or respiration, and/or maximum/minimum valuesrecently recorded. Use of inputs additional to impedance measurementsprovides a potential advantage by constraining conditions of themeasurements so that variables relating to impedance contact quality canbe isolated.

In some embodiments, recorded data (comprising impedance and associatedcondition data) is expressed as a time series such as: X(t)=(Z(t),A(t)), t=t₀, t₁, t₂, . . . , wherein X(t) represents all measurements asa function of conditions and measurements, Z(t) is the impedancecomponent of the measurements, and A(t) represents associated conditionsof the impedance measurements, for example, known anatomical attributes,other prior information, or other simultaneously determined information(for example, organ type, and measurement location).

In some embodiments, X(t) is related to another vector Y(t) describingan assessment of contact with the tissue, based on use of calibrationinformation in correlation data structure 130. Calibration is described,for example, in relation to FIG. 1A, herein. In some embodiments,calibration of the procedure comprises, for example, statisticalanalysis and/or machine learning which determines correlations betweenseparately determined states of Y(t) and X(t). In operation, thesecorrelations are used to select likely existing states described by Y(t)based on observed states of X(t).

At block 256, in some embodiments, dielectric contact quality isreported. Dielectric contact quality is optionally reported according toa scale which either reports Y(t) directly, or is a transform of Y(t).Optionally, dielectric contact quality is reported as a value inarbitrary units, and/or as a value in units which correspond to areference scale, for example, contact force (e.g., in units ofequivalent force, equivalent gram-force, or another reference-equivalentunit). Optionally, dielectric contact quality is reported as acategorizing assessment of contact quality. In some embodiments, thecategories comprise:

-   -   Insufficient dielectric contact quality (for achieving the        purpose at hand, for example, lesioning);    -   Sufficient dielectric contact quality (for the same purpose);        and/or    -   Excessive contact quality (e.g. contact which is associated with        a dangerous amount of contact force, so that there is a        significant risk of perforation or other unintended damage to        the contacted tissue wall).

An example of a simultaneous graphical presentation of dielectriccontact quality information in categorized, arbitrary unit, and contactforce-equivalent form is described herein in relation to FIG. 4.

At block 260, in some embodiments, there may be a side-branch of thecontact quality assessment loop during which ablation—or anotherprocedure to which dielectric contact quality is relevant—is optionallyperformed. Optionally, ablation is performed in parallel with a sequenceof loops passing blocks 250-258; with additional and/or continuingablation performed during each loop. Optionally, entry into block 260and/or control of ablation within block 260 is at least partiallydependent on a dielectric contact quality assessment. For example,initiation of ablation is optionally blocked and/or yields an alert atuser interface 150 if contact quality is insufficient (additionally oralternatively, excessive) for safe and/or reliable lesioning. In someembodiments, an ongoing treatment procedure (such as an ablation) iscontrolled based on contact quality. For example, a power or otherparameter of an ablation treatment (such as power supplied to an RFablation probe) is optionally adjusted in coordination with variationsin contact quality. Optionally, during an ablation, an ablationparameter is adjusted based on changes to contact quality. For example,ablation power is raised to compensate for lowered contact qualityand/or lowered to compensate for higher contact quality (e.g., as mayoccur due to motions of heartbeat and/or respiration). Optionally oradditionally, another ablation parameter is adjusted; for example,frequency, phase, electrode selection, signal timing, or anotherparameter of ablation. This provides a potential advantage for improvinguniformity and/or predictability of lesioning in dynamic conditions. Insome embodiments, whether or not to ablate during a particular loop isdetermined based, for example, on an estimate of contact quality beingin and/or remaining in an acceptable range. If paused, the ablationoptionally continues during a subsequent loop where appropriateconditions are restored.

For reference, it is noted that in catheterized ablation treatment ofatrial fibrillation, a typical targeted time of RF ablation (for each ofan optional plurality of ablation foci) is, for example, within about10-30 seconds, 10-40 seconds, 10-60 seconds, or within another range oftimes having the same, higher, lower, and/or intermediate values. Whenheating tissue to ablate, for example by RF ablation, typical averagepower delivery is, for example, about 10 W, 20 W, 30 W, 35 W, or anotherlarger, smaller, or intermediate value. Typical radio frequencies usedwith RF ablation are, for example, in the range of about 460-550 kHz;and commonly about 500 kHz. It is to be understood that, optionally,another ablation modality is used.

In some embodiments, treatment (ablation heating energy, for example) isdelivered through the same electrode(s) as are used for measurement ofimpedance values reflecting dielectric contact quality with tissue,e.g., as RF energy at a frequency inducing appropriate “resistive”losses in the tissue which result in tissue heating. It is a potentialbenefit to ablate and measure using the same electrodes. For example, itcan result in less instrumentation required, less positioningcoordination required, and/or a more direct relationship betweenmeasurements made and results achieved. Additionally or alternatively,in some embodiments, measurements and ablation are performed by separateinstruments (however, in this case, at least some form of mechanicalcoupling and/or contact between the instrument probes should be providedfor so that the dielectric contact quality measurement is relevant tothe effects of the treatment probe). As also mentioned hereinabove,ablation is optionally by any ablation method known.

At block 258, in some embodiments, a determination is made as to thecontinuation of the procedure. If the procedure continues, flow returnsto block 250. Otherwise, the procedure ends.

Display of Dielectric Contact Quality

Reference is now made to FIG. 4, which illustrates a graphical userinterface (GUI) widget 400 for display of dielectric contact qualityinformation to a user, according to some exemplary embodiments of thepresent disclosure. Optionally, features of GUI widget 400 describedhereinbelow are additionally or alternatively provided by separatedisplays. However, there is a potential advantage to providing a singledisplay to allow at-a-glance status determination.

In some embodiments, a display function of user interface 150 comprisesa display such as GUI widget 400. In some embodiments, GUI widget 400comprises one or more indications of contact quality between a probe111, 112 and a target tissue region 106. In some embodiments, one suchindication comprises a dielectric contact quality scale 402. Optionally,scale 402 distinguishes a plurality of regions (e.g., regions 402A,402B, 402C), which indicate different qualitative contact qualitystates. For example, scale region 402A optionally representsinsufficient contact (e.g., contact ineffective for the production of atherapeutic result). Scale region 402B optionally represents excessivecontact (e.g., contact which represents a potential danger of traumasuch as organ perforation). Scale region 402C optionally represents arange within which contact is sufficient. In some embodiments, a scalemarker 405 is provided which gives a relative quantitative assessment ofcontact quality. The scale is optionally in arbitrary units. Optionally,movement of scale marker 405 along the scale is continuous, or dividedinto unit steps.

In some embodiments of the invention, a force indication 404 is providedas part of GUI widget 400. In some embodiments, force indication 404 isprovided in force-equivalent units (e.g., grams-force). A potentialadvantage of this display is to allow operators to perform proceduresbased on guidelines originally defined in terms of contact force (e.g.,as measured by a probe force sensor), without a requirement to translateinto another unit.

In some embodiments, one or more additional features are providedrelating to dielectric assessment of tissue at a contact region. In someembodiments, dielectric measurement is also used to determine one ormore parameters of the tissue itself. For example, GUI widget 400includes a tissue thickness indication 408 (e.g., giving an estimatedtissue thickness in mm); and/or a lesion depth indicator 406. Lesiondepth indicator 406 optionally comprises a graphical illustration ofmeasured and/or predicted lesion geometry. For example, the peak of thehill arising from the center of indicator 406 optionally represents themaximum depth of a tissue ablation lesion which is currently beingassessed, and/or which is planned for ablation. The circumference of thehill optionally represents an estimated lesion diameter.

It should be understood that the graphical representation of thesefunctions optionally assumes other forms; the specific graphicalrepresentations of GUI widget 400 comprise an illustrative example ofhow various indication functions are optionally combined.

Examples of Dielectric Contact Quality as a Predictor of Contact Force

Reference is now made to FIG. 5, which is a graph presenting estimatesof contact force derived from dielectric contact quality measurements,the estimated contact forces being plotted with respect to directlysensed contact forces, according to some embodiments of the presentdisclosure.

To generate data for this graph, contact force was measured by a forcesensing probe pressed against an ex vivo preparation of myocardialtissue (porcine right ventricle tissue at physiological temperature).Corresponding dielectric contact quality was determined by dielectricproperty measurements, made for example as described in relation to FIG.2 herein, and converted by means of a classifier to a contact forceequivalent. The classifier was constructed based on a separate set ofcalibration measurements, for example as described in relation to FIG.1A, herein. For all measurements, the root mean squared error (RMSE)between actually measured and estimated contact force was about 8.4grams-force.

It can be seen from the graph that the classification results produced astrong linear trend, deviating to an under-estimation (and somewhatlarger error) near the top of the tested force range. This deviationpotentially corresponds to less distinguishable force levels in theupper range; for example, as other parameters of contact to whichdielectric contact quality is sensitive (e.g. area of contact) approachmaximum values.

Reference is now made to FIG. 6, which is a graph of receiver operatingcharacteristic (ROC) presenting for the data of FIG. 5 a true positiverate versus false positive rate for dielectric contact quality-basedestimation of contact force above a threshold of 75 grams-force,according to some embodiments of the present disclosure. It should beunderstood that each point along the ROC graph corresponds to differentmultiparameter dielectric readings which have been mapped to theestimated contact force on which the ROC graph is based.

On an ROC graph, true positive rate corresponds to sensitivity (Y axis;higher is more sensitive), and false positive rate corresponds to1-specificity (X axis; further left is more specific). Perfectclassification (100% sensitivity and specificity) would appear as apoint in the upper left corner of the graph; the diagonal line is theline of no classification (chance). For the 75 grams-force threshold,the graph shows an area under the ROC curve of about 95% of the totalgraph area. This fairly high value appears to corroborate conclusionsdescribed above with respect to FIG. 5.

Reference is now made to FIG. 10, which is a graph presenting dielectricproperty-estimated contact force vs. directly measured force, accordingto some exemplary embodiments of the invention.

On the vertical axis, values represent the returned contact forceestimate (in grams-force) of a contact force estimator operating ondielectric measurements. On the horizontal axis, values representgrams-force measured by a TactiCath™ catheter probe from St Jude Medical(legacy Endosense system). Measurements were made with respect tocontact with porcine left atrium wall. Open (white centered) plot pointsrepresent corresponding data points (measurements made through the samecatheter, either dielectrically or via the force sensor). Darkened(gray-centered) plot points represent the unity line of the direct forcemeasurements plotted against themselves.

Reference is now made to FIGS. 11A and 11C, which graph contact forcemeasurements using a TactiCath™ catheter (as described in relation toFIG. 10). Reference is also made to FIGS. 11B and 11D, which graphcontact quality level estimates made based on dielectric measurements(also as described in relation to FIG. 10). The epochs in minutes ofFIGS. 11A-11B correspond to one another; as is also the case for FIGS.11C-11D. In FIGS. 11B and 11D, the contact levels are set between 0 and1.0 for estimated contact forces below 10 grams-force; between 1.0 and2.0 for estimated contact forces between 10 and 25 grams-force; between2.0 and 3.0 for estimated contact forces between 25 grams-force and 40grams-force, and between 3.0 and 4.0 for estimated contact forces above40 grams-force.

Reference is now made to TABLE 1, which displays in tabular form datafrom the experiments outlined in FIGS. 10-11D. The data from bothmeasurement types (directly measured contact force and estimated contactquality) have been converted to force levels of low, optimal, high andexceed, which use the same respective thresholds (<10 grams-force, 10-25grams-force, 25-40 grams-force, and >40 grams-force) as are also shownin FIGS. 11B and 11D. It should be noted that the estimated contactquality categorization may be considered “safe” with respect to valuesin the “exceed” category (the category of potentially unsafe levels ofcontact force), since the estimator makes the “exceed” categorization atthe same level of contact, or a lower level of contact, than thecategorization based on the measured contact force.

TABLE 1 MEASURED CONTACT FORCE CATEGORY Low Optimal High ExceedESTIMATED Low 87%  3% CONTACT Optimal 13% 85% 10% QUALITY High 12% 85%12% CATEGORY Exceed  5% 88%

3-D GUI Widget for Organ View Orientation

Reference is now made to FIG. 7A, which schematically illustrates a viewof a graphical user interface (GUI) widget 700, representative of the3-D orientation of the atria of a heart in space, according to someembodiments of the present disclosure. Reference is also made to FIG.7B, which schematically illustrates a heart 750 in an orientationcorresponding to the orientation of GUI widget 700, according to someexemplary embodiments of the present disclosure.

In some embodiments, a GUI widget 700 comprises a schematic graphicalrepresentation of an anatomical structure; for example, at least aportion of a heart 750. The schematic graphical representation isoptionally implemented, for example, as a 3-D model and/or as a set of2-D icons representing views of the anatomical structure in differentorientations. In some embodiments, the widget 700 comprises a dynamicicon, changing appearance according to a virtual orientation of theschematic graphical representation. In some embodiments, the schematicgraphical representation includes one or more reference bodies (forexample, atrial representations 702, 704); distinguishable in theirorientation by their spatial relationships to each other, and/or by oneor more indicating features (e.g. vascular segments 712 and 714, and/orvalve indicators 722 and 724). Optionally, the indicating featuresprotrude from the reference bodies 702, 704. In this and followingexamples, shading is also used as a distinction, with the right atrium752 or its right atrial representation 702 (and associated features)being shaded in light gray, and the left atrium 754 or its left atrialrepresentation 704 (and associated features) being shaded in dark gray.Optionally, color, texture, or another aspect of visual appearance isused to help emphasize distinctions. For example, the left atrium isoptionally colored red and/or orange, and the right atrium blue and/orgreen.

Optionally, atrial representation 702 corresponds to right atrium 752 ofa heart 750, atrial chamber representation 704 corresponds to leftatrium 754 of a heart 750, vascular segments 712 correspond to rightatrium connected segments of the superior and/or inferior vena cava 762,vascular segments 714 correspond to left atrium connected segments ofthe pulmonary veins 764, valve indicator 722 corresponds to thetricuspid valve leading from the right atrium 752 to right ventricle772, and/or valve indicator 724 corresponds to a mitral valve leadingfrom left atrium 754 into left ventricle 774.

In some embodiments, GUI widget 700 is provided as a reference forassisting determination of the orientation of a corresponding view of aheart 750. For example, GUI widget 700 is displayed on a screenalongside a view of heart 750, in a 3-D orientation suitablycorresponding to the displayed 3-D orientation of heart 750.

Optionally, widget 700 is linked to GUI inputs so that it also acts asan orientation control. For example, event handling software connectedwith GUI widget 700 is configured to receive click, drag, touch, swipe,and/or any other suitable user input gesture directed to (e.g., on,alongside, and/or passing over) the displayed GUI widget 700.Optionally, the event handling software in turn induces rotation of thedisplayed view of GUI widget 700 and an associated view of heart 750 insynchrony, based on the user input gestures. Optionally, events areinterpreted as simulating physical interaction; for example, simulatingrotation as if motion gestures are contacting the displayed surface ofthe GUI widget and causing it to rotate in the gesture direction.Optionally, the event handling software defines hotspots for selectionof particular views. For example, clicking on (or otherwise indicating)a particular region of GUI widget 700 optionally triggers re-orientationof that region to face the operator. Additionally or alternatively,indicating a particular region alongside GUI widget 700 triggers arotational step (for example a change in orientation of 90°). In someembodiments, rotation of GUI widget 700 is triggered by input events toother controls/display elements; for example, gestures which simulatedirect manipulation of a view of the heart 750, inputs to sliders,automatic view changes in response to navigation movements of a catheterprobe, etc. It should be understood that the input and handling examplesprovided are non-exhaustive, and not limiting of the scope of theconcept.

In some embodiments, GUI widget 700 is used to assist in manipulatingand/or comprehending an anatomically correct view of a heart 750,optionally in conjunction with the positioning and orientation oftreatment tools, such as catheter probes. Even though the physician iswell familiar with the anatomy of an organ targeted for treatment,computer-visualized surgery can present a very wide range of views whichmay themselves create opportunities for confusion. For example,anatomical views are optionally presented as solid, transparent,partially transparent, and/or cutaway images; each of which obscures orreveals anatomical landmarks in different ways. Additionally oralternatively, views can be presented at different scales: for example,whole-organ displays, and/or magnified views of an organ in the vicinityof a region targeted for treatment. Magnified views in particular areprone to creating confusion over position and/or orientation, since keylandmarks providing visual context may be out of the frame of view.Optionally, color data is superimposed on anatomical shape data, forexample, to indicate tissue health, thickness, and/or another feature.Some organs, and in particular the heart, are in constant motion, whichmovement in a view display optionally reflects. Moreover, structuressurrounding and/or connecting to an organ (particularly in the case ofthe multiply connected heart) are optionally represented visually tovariable extents of completeness from case to case, and/or applicationto application, which can also influence the appearance of a targetorgan in context. It is finally mentioned that an unfamiliar orientationor an unusual distortion of an organ view can itself give rise touncertainty. For example, the orientation of the heart in FIG. 7B(corresponding also to view 791 of FIG. 7D) is not as usually shown inanatomical textbooks, but rather shown as seen from beneath, withventral side up, and dorsal side down. View 796 of FIG. 7D is alsounusual, being an upside-down dorsal view of a heart 750.

Optionally, features selected to help mark orientation of GUI widget 700correspond to (without necessarily anatomically duplicating in detail)anatomical features which a physician is likely to be concerned withduring treatment. Potentially, this helps to reduce the “cognitivedistance” between what the physician is really looking for, and what theGUI widget 700 directly represents. For example, catheter-guidedtreatment of atrial fibrillation by cardiac tissue ablation optionallycomprises aspects such as: reaching the right atrium 752 via a branch ofthe vena cava 762, crossing the septal wall between atria for access totreatment locations within the left atrium 754, and ablation from withinthe left atrium 754 of one or more regions defined by the positions ofthe pulmonary veins 764. Each of these anatomical features is optionallyrepresented by corresponding features of GUI widget 700, for example asidentified hereinabove. In contrast, it is a potential advantage tosuppress features which are not directly relevant to tasks of thetreatment itself, even if these are anatomically and/or functionallyimportant otherwise. For example, GUI widget 700 optionally indicatesthe positions of the tricuspid valve and mitral valve (by valveindicators 722 and 724, respectively), but optionally omits showing theventricles to which they connect. It is also a potential advantage toavoid an excess of detail even in features that are represented: forexample, the degree of schematic representation in FIG. 7A is such thatthe valves are represented only by bulges. Indeed, an alternativeinterpretation of valve indicators 722, 724 is as shrunkenrepresentations of the ventricles themselves.

Optionally, features of the 3-D model underlying GUI widget 700, and/orof its presentation, are provided to create a relatively consistent,rotationally distinct, appearance. Suppression of the ventricles 772,774, for example, provides a potential advantage by reducing thetendency of the ventricles to obscure the atrial representations 702,704 and their vascular landmarks 712, 714. Landmarks are preferablyprovided in sufficient density for identification at any orientation,without over-providing to the point that the landmarks become themselvesdistracting. Optional coding of structures by color and/or shadingpotentially helps to make it clear at a glance at least the generalorientation of the GUI widget 700.

Optionally, GUI widget 700 is constructed using shapes and/or shaperelationships suggestively corresponding with shapes of actual anatomy,even though they do not literally depict them. The shapes optionallycomprise an assemblage of basic geometrical figures. Vascularstructures, for example, are optionally represented as straight tubes orcylinders; chambered structures as ellipsoids; aperture structures (suchas valves) as flattened ellipsoids, etc. Optionally representation as amesh structure is used. Use of mesh model may allow closer approximationof actual heart anatomy to be achieved. However, a potential advantageof representing identified features as simple geometrical objects isthat they remain easily identifiable and/or clearly distinctive from awide range of viewpoints. Furthermore, such shapes potentially help tofree the widget from irrelevant (non-differentiating) visualinformation.

In some embodiments, a rough size difference among features helps tocreate an orienting asymmetry and/or readier identifiability.Optionally, such differences are selected to evoke similar differencesin the actual anatomy. For example, right atrial representation 702 isshown slightly smaller than the more oblong left atrial representation704, while the vena cava branches 712 are shown larger than thepulmonary vein branches 714. Such correspondences with anatomicalrelationships are not necessarily quantitative depictions of dimensionratios. However, they potentially serve a mnemonic function, byschematically evoking salient details of the actual anatomy whilerequiring a minimum of cognitive load to be identified. Reference is nowmade to FIG. 7C, which shows views 741, 742, 743, 744, 745, 746 of sixdifferent orientations of GUI widget 700, separated by about 90° fromeach other, according to some exemplary embodiments of the presentdisclosure. Reference is also made to FIG. 7D, which shows the views ofFIG. 7C reduced in size, alongside corresponding anatomical views 791,792, 793, 794, 795, 796 of a heart 750, according to some exemplaryembodiments of the present disclosure.

Arrows 730 may be understood as indicating rotation of GUI widget 700and/or heart 750 by about 90° between the view at the base of eacharrow, and the view at the tip. The rotation may be understood as a 90°roll, comprising rotation of the surface portion nearest the viewer'sposition to a perpendicular orientation on the side of the rotated GUIwidget 700 which is away from the arrow tip.

Heart view 791 and GUI widget view 741 correspond to the view of FIGS.7A-7B. Both the light-shaded right atrium 752 and dark-shaded leftatrium 754 are clearly visible in the anatomical view 791.

Heart view 793 shows a conventional, top side up ventral view of a heart750, with the right atrium 752 clearly visible, but the left atriumlargely hidden. The corresponding view 743 of the GUI widget 700,however, shows both atria clearly. Moreover, it is easy to tell byglancing at views 741 and 743 how the two views relate to one another,since most of features remain plainly visible in each. In heart views791, 793, the changing orientation leads to radical changes in apparentshape, and/or changes in which anatomical features are visible. Similarobservations apply to comparisons involving views of the otherorientations. It can be understood that the difference in ease ofcomprehension potentially becomes still more pronounced whendifferential shading of the heart views (shown herein primarily forpurposes of explanation) is removed and/or replaced with shading servingsome different purpose.

Another potential advantage of the GUI widget 700 is seen mostparticularly in connection by consideration of the sequence of views742, 743, and 744. Shading of the GUI widget as viewed from the side ofleft atrium (view 742) is almost completely dark (using the shadingconventions illustrated), while shading as viewed from the opposite side(view 744) is almost completely light. About equal balance between thetwo shadings is seen in ventral view 743. These gross differences can bediscerned even in peripheral vision, which is a potential advantage foran operator whose visual attention is focused on a nearby anatomicaldisplay.

The anatomical views 791, 792, 793, 794, 795, 796 of heart 750 are shownall at the same scale. However, it should be understood that the sameorientation information is shown, in some embodiments, as the anatomicalview is magnified. Optionally, some indication of such scale changes areoptionally also provided on GUI widget 700. For example, a region ofviewing indicator (a rectangle, for example) is optionally superimposedon the GUI widget 700 to indicate which part of the represented anatomyis being closely inspected. Optionally, a view from within an organ (forexample, from within an atrium) is indicated by modification of the GUIwidget 700, for example, by suppressing display of the GUI widgetportions representing anatomy which is “behind” the viewing port of theanatomy.

Indicators for Monitoring of Lesion Status

Reference is now made to FIGS. 8A-8E, which illustrate a display forindicating lesioning status, including contact force, to a user,according to some exemplary embodiments.

FIGS. 8A-8E comprise an artificially rendered image of an ablation probe802 and its position relative to tissue 805 near to which ablation probe802 is positioned for ablation. Optionally, the rendering is in colorsimilar to the vital color of the tissue (black and white is shown forpurposes of illustration). In some embodiments, the rendering includes avisual indication of contact pressure between the tissue 805 and theelectrode 802 comprising an indented region 804. For example, indentedregion 804 is shown more strongly deflected in FIG. 8B than in FIG. 8A(and not deflected at all in FIG. 8D), providing an indication ofrelative contact force. Optionally, the depth to which indented region804 is actually shown indented is variable depending, for example, on ameasured contact force and/or contact quality value.

In some embodiments, an estimate of a quality of the lesion which wouldbe and/or is being formed at a current site of contact is provided by avisual indication, such as circle 813. In FIGS. 8D-8E, additionalindication 810, 812, and 814 are also shown, indicating full or partialdegrees of transmural lesioning as estimated based on pre- orpost-lesion measurements. More details of such indications used for oneor both of pre- and post-lesioning tissue assessment for transmuralityof a lesion are discussed, for example, in relation to FIG. 9.

In some embodiments, one or more additional indications are provided aspart of the rendered image which provide an indication of how lesioningis proceeding. For example, in FIG. 8B, “steam” is shown arising fromthe lesion point. Optionally, this is an indication that temperature hasreached (and/or is maintained at) a certain threshold. The threshold maybe, for example, a threshold at which lesioning occurs, a thresholdabove which a danger of effects such as steam pop or charring occurs, oranother threshold. In FIG. 8C, tissue 805 is shown relatively bleachedin color, which optionally serves as an indication of the currentestimated extent of lesioning.

Reference is now made to FIG. 9, which illustrates display elements 810,812, 813, 814 which are optionally used to indicate estimatedtransmurality of a lesion to a user, based on pre- and post-lesioningdielectric property measurements.

In some embodiments, estimated transmurality is communicated to a userby the use of a simplified graphical element. The elements of FIG. 14take the form of complete circles 813, 814, to indicate a positiveestimate of lesion transmurality, and the form of incomplete circles812, 810 (e.g., ¾ circles) to indicate a negative estimate of lesiontransmurality. Optionally, inner circles 812, 813 are used to indicateestimates based on pre-lesioning measurements. Optionally, outer circles810, 814 are used to indicate estimates based on post-lesioningmeasurements.

It is expected that during the life of a patent maturing from thisapplication many relevant transcatheter treatments will be developed;the scope of the term “transcatheter delivery of a disease treatment” isintended to include all such new technologies a priori.

As used herein with reference to quantity or value, the term “about”means “within ±10% of”.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean: “including but not limited to”.

The term “consisting of” means: “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

As used herein, the singular form “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a compound” or “at least one compound” may include a pluralityof compounds, including mixtures thereof.

The words “example” and “exemplary” are used herein to mean “serving asan example, instance or illustration”. Any embodiment described as an“example” or “exemplary” is not necessarily to be construed as preferredor advantageous over other embodiments and/or to exclude theincorporation of features from other embodiments.

The word “optionally” is used herein to mean “is provided in someembodiments and not provided in other embodiments”. Any particularembodiment of the invention may include a plurality of “optional”features except insofar as such features conflict.

As used herein the term “method” refers to manners, means, techniquesand procedures for accomplishing a given task including, but not limitedto, those manners, means, techniques and procedures either known to, orreadily developed from known manners, means, techniques and proceduresby practitioners of the chemical, pharmacological, biological,biochemical and medical arts.

As used herein, the term “treating” includes abrogating, substantiallyinhibiting, slowing or reversing the progression of a condition,substantially ameliorating clinical or aesthetical symptoms of acondition or substantially preventing the appearance of clinical oraesthetical symptoms of a condition.

Throughout this application, embodiments of this invention may bepresented with reference to a range format. It should be understood thatthe description in range format is merely for convenience and brevityand should not be construed as an inflexible limitation on the scope ofthe invention. Accordingly, the description of a range should beconsidered to have specifically disclosed all the possible subranges aswell as individual numerical values within that range. For example,description of a range such as “from 1 to 6” should be considered tohave specifically disclosed subranges such as “from 1 to 3”, “from 1 to4”, “from 1 to 5”, “from 2 to 4”, “from 2 to 6”, “from 3 to 6”, etc.; aswell as individual numbers within that range, for example, 1, 2, 3, 4,5, and 6. This applies regardless of the breadth of the range.

Whenever a numerical range is indicated herein (for example “10-15”, “10to 15”, or any pair of numbers linked by these another such rangeindication), it is meant to include any number (fractional or integral)within the indicated range limits, including the range limits, unlessthe context clearly dictates otherwise. The phrases“range/ranging/ranges between” a first indicate number and a secondindicate number and “range/ranging/ranges from” a first indicate number“to”, “up to”, “until” or “through” (or another such range-indicatingterm) a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numbers therebetween.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

1-41. (canceled)
 42. A method of characterizing contact quality betweena target tissue and an intra-body probe comprising a plurality ofelectrodes, the method comprising: measuring a plurality of dielectricproperties of the environment of electrodes of the intra-body probe,using an electrical circuit comprising the target tissue and theplurality of electrodes of the intra-body probe; wherein the measuringcomprises carrying out measurements of a plurality of electrical fieldfrequencies by the plurality of electrodes of the intra-body probe; andcharacterizing contact quality between the target tissue and theintra-body probe by mapping the plurality of measured dielectricproperties to a value in a range indicating a measure of contactquality.
 43. The method of claim 42, wherein the intra-body probe isflexible and carries a plurality of electrodes, and the flexibility ofthe probe allows the plurality of electrodes to be positioned along aportion of the target tissue.
 44. The method of claim 42, wherein theintra-body probe makes a plurality of simultaneous contacts with thetarget tissue, and the characterizing comprises separatelycharacterizing each of the plurality of simultaneous contacts.
 45. Themethod of claim 44, wherein the intra-body probe comprises an ablationelectrode, and wherein the method comprises operating the ablationelectrode to ablate at each of the plurality of simultaneous contactsunder separate control, based on the corresponding characterizing ofcontact.
 46. The method of claim 42, wherein the characterization of thecontact comprises mapping of the measured dielectric properties to amapped value within a range of values characterizing the contactquality, and the mapped value comprises an index characterizing contactquality.
 47. The method of claim 42, wherein the characterization of thecontact comprises mapping of the measured dielectric properties to amapped value within a range of values characterizing the contactquality, and the mapped value represents a contact force equivalent,such that a force of contact of the intra-body probe with the targettissue is represented by the mapped value.
 48. The method of claim 42,wherein the intra-body probe comprises the electrode defining theelectrical circuit.
 49. The method of claim 48, wherein the estimationof an equivalent force of contact is substantially independent of anangle of contact between the probe and the surface of the target tissue.50. The method of claim 49, wherein the equivalent force of contactchanges by less than 10% through a range of angles of contact, and therange of angles of contact is within 45° of a central angle of contact.51. The method of claim 42, wherein the characterizing comprisesestimation of an equivalent force of contact of the probe with a surfaceof the target tissue, and the method comprises providing a user feedbackindicating the equivalent force of contact.
 52. The method of claim 42,comprising operating an ablation electrode based on the characterizationof the contact and wherein the operating of the ablation electrode isgated to occur only when the characterized contact is within apredetermined range.
 53. The method of claim 52, wherein thecharacterizing contact is performed iteratively during operating of theablation electrode.
 54. The method of claim 42, comprising operating anablation electrode, wherein the operating of the ablation electrode isbased on an estimated contact force of the characterized contact, suchthat at least one of an ablation power, a duration of ablation, aselection of an electrode, and a frequency of ablation energy, isselected based on the estimated contact force.
 55. The method of claim42, wherein the characterizing comprises evaluating a risk ofperforation of the target tissue by the probe, and the method comprisingproviding a user feedback indicating the risk of perforation.
 56. Themethod of claim 42, wherein the characterizing contact is based on adata structure mapping measured dielectric properties to acharacterization of contact with the target tissue.
 57. The method ofclaim 56, wherein the data structure comprises machine-learnedassociations applicable to the measured dielectric properties to convertthem to the characterization of contact with the target tissue.
 58. Adevice for ablation of a target tissue based on dielectric contactquality of an intra-body ablation probe with the target tissue,comprising: the intra-body ablation probe, including a plurality ofelectrodes; an electrical field measurement device, configured tomeasure dielectric properties in the environment of the plurality ofelectrodes based on signals sensed by a plurality of electrode pairs ofthe plurality of electrodes and at a plurality of frequencies; and acontact characterization module, configured to characterize contactbetween the intra-body ablation probe and the target tissue, based onthe dielectric properties measured by the electrical field measurementdevice.
 59. The device of claim 58, wherein the contact characterizationmodule comprises a data structure mapping the dielectric properties tocharacterization of contact.
 60. The device of claim 59, wherein thedata structure comprises machine-learned associations applicable to themeasured dielectric properties to convert them to the characterizationof contact with the target tissue.
 61. The device of claim 58,comprising a display configured to display the characterized contact asan estimate of contact force.
 62. The device of claim 58, wherein theintra-body probe is flexible and carries a plurality of electrodes, andthe flexibility of the probe allows the plurality of electrodes to bepositioned along a portion of the target tissue.
 63. The device of claim58, wherein the intra-body probe is configured to make a plurality ofsimultaneous contacts with the target tissue, and the characterizingcomprises separately characterizing each of the plurality ofsimultaneous contacts.
 64. The device of claim 62, wherein theintra-body probe is configured to make a plurality of simultaneouscontacts with the target tissue, and the characterizing comprisesseparately characterizing each of the plurality of simultaneouscontacts.
 65. The device of claim 58, further comprising at least oneprocessor configured to gate the operation of an ablation electrode tooccur only when the characterized contact is within a predeterminedrange.
 66. The device of claim 58, wherein the contact characterizationmodule is configured to estimate an equivalent force of contactindependently of an angle of contact between the probe and the surfaceof the target tissue.
 67. The device of claim 66, wherein the equivalentforce of contact changes by less than 10% through a range of angles ofcontact, and the range of angles of contact is within 45° of a centralangle of contact.